This invention relates to bushings for injection molding systems wherein the bushings have a controllable gate or orifice.
Injection molding bushings are utilized to transfer molten plastic material from an injection molding machine into the cavity of a mold. The bushings are positioned in molds attached to platens of the injection molding machine and are adapted to transfer the molten plastic material from the nozzle of the injection molding machine barrel to the mold cavities.
The mold bushings, often called xe2x80x9csprue bushings,xe2x80x9d can be unheated or heated. Unheated bushings leave an elongated sprue on the molded part which normally has to be trimmed or cut off. Heated bushings, which leave little if any sprue on the part, can be centrally heated or externally heated and can also have pins or other shut-off mechanisms for opening and closing the gate or orifice as required.
Internally heated mold bushings can have a heated torpedo-like member positioned in the flow stream. Bushings of this type are shown, for example, in U.S. Pat. Nos. 3,010,155 and 4,161,386. Mold bushings which are heated externally can have annular heating elements positioned around a central flow passageway. These are shown, for example, in U.S. Pat. Nos. 4,273,525 and 4,266,723. The heating elements can be coil heaters, cast heaters, or conventional band-type heaters, all of which maintain the plastic material in the bushing in a molten condition.
Many of the mold bushings have gates or orifices which are controlled by a pin-type mechanism or the like to open and close the orifice in accordance with the desired process for filling the mold. The pin members are typically controlled by a motorized or automatic mechanism of some type, such as shown in U.S. Pat. Nos. 4,095,931 or 4,279,582.
In known valve gate-type bushings, all or a substantial portion of the pin member is contained within the molten plastic flow. The pin member partially divides the mass of plastic material in the bushing which often causes undesirable features in the molded parts, such as blemishes and weld lines. With some materials, the pin member prevents satisfactory intermixing of the material. Also, the pin member can result in the formation of shear planes in the molten material which can cause unsightly blemishes or lines in the final part, and may cause areas of weakness in the final part.
Some bushings which have partially solved these problems are shown, for example, in U.S. Pat. Nos. 4,925,384 to Manner, and U.S. Pat. No. 4,412,807 to York. However, the ""384 patent does not adequately separate the material from the moving pin member thus creating unsightly or unwanted defects in the final part. Also, the ""807 patent contains several additional machined components creating a more costly and complex device.
It is an object of the present invention to provide an injection molding bushing which is an improvement over known bushings. It is another object of the present invention to provide an improved bushing member which is easier and less costly to manufacture.
It is a further object of the present invention to provide a mold bushing which completely separates the shut-off pin from the material flow in the bushing. It is a still further object of the present invention to provide an improved mold bushing which does not contain any components or structure which separate the flow of material therein and thus which creates a final product which is more acceptable, both in aesthetics and strength.
These and other objects and purposes of the present invention will become apparent from the following description of the invention, when viewed in accordance with the attached drawings and appended claims.
In general, the present invention provides a mold bushing with an integral one-piece body member having an external heating member and separate passageways for the material flow and for the shut-off pin. The mold bushing body member is preferably externally heated around its periphery by a cast heating member, although other conventional types of heating members can also be utilized. The body member preferably has a separate tip or end member in which the orifice (or gate) is situated. The tip member also has a central discharge chamber. The pin member is centrally positioned in the body member and is adapted to mate with and open/close the gate or orifice. The flow passageway is substantially parallel to the passageway in which the gate pin is positioned and operates to receive and transfer the molten plastic material from an injection molding machine and/or manifold into a mold cavity.
A separate wear bushing member, preferably is provided and positioned adjacent the body member in the discharge chamber. The wear bushing member has an indexing member and fills a substantial portion of the discharge chamber in the tip assembly. This keeps the plastic material from degrading prior to being injected into the mold cavity.
In an alternate embodiment, the body member is extended into the discharge chamber and a separate cylindrical wear bushing is provided in the end of the body member in order to support the end of the gate pin. In another embodiment of the invention, the gate or orifice is provided in the mold die creating a xe2x80x9ctoplessxe2x80x9d-type of mold bushing arrangement.
In another alternative embodiment, a solid end insert member is provided with substantially parallel channels or passageways for the pin member and molten plastic material which converge at an orifice at the tip of the end insert member. A threaded sleeve member is threadedly attached to the lower end of the body member and securely holds the end insert member in place.
These and other features, benefits and advantages of the present invention will become apparent from a review of the following description of the invention, when viewed in accordance with the attached drawings and appended claims.